The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
Handrails are a known and standard part of any escalator, moving ramp, moving walk or other similar transportation apparatus. Conventionally, such handrails are formed largely of rubber, which makes up the outer cover of the handrail and forms a comfortable exterior “C” shape to be grasped by a user, and also include steel reinforcing cables and fabric plies, which act to provide dimensional stability to the handrail.
To locate the handrail and enable it to travel freely, it is provided with a T-shaped slot on the underside. This slot engages a corresponding T-shaped section or guide made from polished steel, plastic or the like and provided along the escalator, and at either end is engaged by large pulley wheels, curved guides, or rollers. Underneath the escalator, appropriate drive mechanisms are provided. To enable the handrail to slide freely, the T-shaped slot is conventionally lined with a fabric, which may be cotton or a synthetic material, which is usually referred to as a “slider”.
Additionally, handrails are usually reinforced longitudinally with steel cables or other relatively inextensible material, as a stretch inhibitor to provide sufficient resistance to stretching in the longitudinal direction. A handrail requires the incorporation within the body of the handrail of a number of reinforcing elements, or plies, to make the handrail sufficiently stiff, at least laterally, to resist both accidental and deliberate derailment of the handrail from the guide, while not detracting from its longitudinal flexibility. These plies are usually fabric having orthotropic properties, that is, they exhibit a certain degree of stiffness in one direction while remaining more flexible in the other. The stretch inhibitor at least must be reasonably precisely located and, more importantly, should generally be located at a uniform depth on a common neutral bending axis, so as to enable the handrail to flex freely as it passes around pulleys etc. The handrail requires the formation of a T-shaped slot, which additionally has to be provided with a slider layer, which is bonded on just one side to the handrail. The T-shaped slot must be accurately formed, to ensure that the handrail is securely retained in position in use.
Because of these requirements, handrails have traditionally been manufactured in a piece wise manner. This has also required the use of rubberized fabric. The plies of rubberized fabric, cords and raw rubber are stacked together, assembled in a mold and compression molded under heat and pressure to cure and mold the composite into the characteristic handrail C-shape. The mold is typically of the order of 10 to 20 feet long, enabling such lengths of handrail to be molded at once. Once each section has been molded, the handrail is moved forward by the length of the mold. The next section is then molded. In this manner the entire length of a single handrail is fabricated and cured except for approximately 5 feet at each end; these ends are then spliced together, molded and cured to form an endless handrail. This manufacturing process is laborious, requires considerable manual labour, and leads to a production rate dictated by the speed of curing reaction of the rubber, typically of the order of 10 minutes, and the length of the mold.
A handrail in use is located on a T-section member. The ability of a handrail to withstand accidental or deliberate displacement depends to a significant extent on the lateral stiffness or lip-strength of the handrail. A major component of an extruded handrail is the elastomeric material, and a key factor is the hardness of the elastomeric material. Selection of the hardness of the elastomeric material, as well as other materials, is a compromise between lateral stiffness and longitudinal flexibility. The handrail must have sufficient longitudinal flexibility to enable it to follow a handrail guide around turnarounds at the ends of an escalator or moving walk. It must also be capable of following the various pulleys through the drive mechanism and back underneath the handrail.
Despite these requirements, as a handrail has a uniform cross-section, it theoretically could be made in continuous lengths, for later cutting to size for individual applications; thus it can be suited to production by an extrusion technique.
U.S. Pat. No. 4,087,223 to Angioletti et al. discloses an extrusion device and the continuous manufacture of a handrail of elastomeric material, C-shaped in cross section. The extrusion device is provided with separate and distinct openings for the introduction of the various elements of the handrail, and with means which shape continuously said elements and arrange them continuously in mutual correct position into elastomeric material.
U.S. Pat. No. 6,237,740 to Weatherall et al. discloses a moving handrail construction, for escalators, moving walkways and other transportation apparatus having a generally C-shaped cross-section and defining an internal generally T-shaped slot. The handrail is formed by extrusion and comprises a first layer of thermoplastic material extending around the T-shaped slot. A second layer of thermoplastic material extends around the outside of the first layer and defines the exterior profile of the handrail. A slider layer lines the T-shaped slot and is bonded to the first layer. A stretch inhibitor extends within the first layer. The first layer is formed from a harder thermoplastic than the second layer, and this has been found to give improved properties to the lip and improved drive characteristics on linear drives.